A standard single-control mixing valve has as described in German patent 3,426,236 of M. Pawelzik et al an upwardly directed stem extending along a stem axis and movable relative to a normally stationary valve axis for regulation of flow through the valve. This stem is controlled by a lever formed with a downwardly open socket that fits complimentarily over the stem so that tipping and pivoting the lever operates the valve. The lever is secured to the stem by a screw that passes through the lever and is threaded coaxially into the stem. A removable cap or cover disk on the lever hides this screw.
While this system is fairly simple and does provide a fairly solid connection between the lever and the valve stem, the cap covering the screw is often found to spoil the appearance of the lever. Furthermore if this cap is pried out and replaced, it is frequently marred somewhat, further ruining the appearance of the fixture.
It has been suggested in German utility model 9,01,658 published 20 June 1991 to simply make the lever a tight snap fit on the valve stem. This system is more attractive, but has been found to provide an insufficiently strong mounting, so that the lever can be knocked off accidentally.